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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 July 2019) | Viewed by 39101

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Dr. Donghoon Kang

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Railroad Safety Research Team, Korea Railroad Research Institute (KRRI), Uiwang, Gyeonggi-do 16105, Republic of Korea
Interests: nondestructive testing and evaluation skills; field application using structural health monitoring techniques; development of fiber optic sensors and field applications; convergence with internet of things technology
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Dear Colleagues,

Traditional non-destructive inspection techniques, such as ultrasonics, electromagnetics, radiography, optical and thermal methods, have contributed to ground-breaking improvements in safety in many industrial areas over the last decade. Even though the demodulation principal is different, these techniques are based on a scheme of defect inspection, denoted as diagnosis. However, estimating the structural health condition at an earlier stage is needed, where damage has not yet been generated, by using in-situ monitoring techniques for the prognosis of structural health during operation. Likewise, the meaning of non-destructive has been gradually expanded from traditional defect inspection to in-situ health monitoring of structures. Due to this reason, there has been a great deal of research on the aforementioned prognosis techniques, as well as on those relating to traditional diagnosis techniques in the non-destructive inspection area over the last decade. Assuming that many things are related to the successful in-situ monitoring of structures, we need to develop more advanced sensors, data acquisition skills, signal processing tools, etc., for a higher level of understandings regarding structures.

We invite you to submit high-quality research, or technical or review papers, to this Special Issue, with an emphasis on innovative new and emerging technologies for a wide range of non-destructive inspection techniques, including in-situ health monitoring.

Some area of interests for this Special Issue include, but are not limited to, new skills and application results of non-destructive testing and evaluation, inspection and analysis, in-situ health monitoring, and convergence with other technologies, such as the Internet of things. In addition, related theory, modelling, and simulations can be included.

The objective of this Special Issue is to gather the experience of leading scientists, researchers, and field engineers. In addition, it can be helpful for people who would like to adopt a new non-destructive inspection system for better safety, as well as production efficiency in industrial fields. From this point of view, we believe that this Special Issue will provide technological advances, and the latest research on the state-of-the-art, as well as innovative field application results in non-destructive inspection, including in-situ health monitoring. Interested and committed individuals from academia, research laboratories, industries, and related companies are invited to contribute by submitting papers to this Special Issue.

If you need any further information about this Special Issue, please do not hesitate to contact me.

Dr. Donghoon Kang
Guest Editor

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Keywords

non-destructive testing (NDT)
non-destructive evaluation (NDE)
non-destructive characterization
new inspection skills
new analyzing skills
modeling and simulation
theory and mechanism
smart structures and integrated systems
Industrial and commercial applications
ultrasonics, electromagnetics, radiography, optical and thermal method
structural health monitoring (SHM), condition monitoring (CM)
Nano-, Bio-, Info-Tech-, and advanced sensors for NDT
non-destructive inspection for Industry 4.0

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Published Papers (13 papers)

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Research

13 pages, 4056 KiB

Open AccessArticle

Effect of Steel Plates on Estimation of the Compressive Strength of Concrete via Ultrasonic Testing

by Hong Chul Rhim, Dae You Kim, Chang Shik Cho and Do Hyun Kim

Materials 2020, 13(4), 887; https://doi.org/10.3390/ma13040887 - 17 Feb 2020

Cited by 9 | Viewed by 2399

Abstract

The presence of embedded steel affects the estimates obtained for the compressive strength of concrete during ultrasonic testing, as it increases the ultrasonic wave velocity. Thus, if the presence of steel in concrete is inevitable, then a correction factor is required for an accurate estimation of the concrete strength. While previous studies focused on the effect of steel reinforcing bars on the speed of ultrasonic waves in concrete, this work expands on the significance of embedded steel from steel bars to include steel plates. The wave velocity was measured for varying dimensions of embedded steel plates from 15 mm to 150 mm using 54-kHz ultrasonic testing equipment. Through experiments, the effect of steel plates on the ultrasonic testing of concrete was quantified to derive proper correction factors. It was found that the thickness, depth, and height of the steel plates significantly affected the test results. These findings can be applied to ultrasonic testing to estimate the compressive strength of concrete consisting of a significant volume of steel, such as in steel-reinforced concrete structures. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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16 pages, 6256 KiB

Open AccessArticle

Displacement, Strain and Failure Estimation for Multi-Material Structure Using the Displacement-Strain Transformation Matrix

by Hye-Lim Jang, Dae-Hyun Han, Mun-Young Hwang, Donghoon Kang and Lae-Hyong Kang

Materials 2020, 13(1), 190; https://doi.org/10.3390/ma13010190 - 2 Jan 2020

Cited by 3 | Viewed by 3569

Abstract

In this study, we propose a method to estimate structural deformation and failure by using displacement-strain transformation matrices, i.e., strain-to-displacement transformation (SDT) and displacement-to-strain transformation (DST). The proposed SDT method can be used to estimate the complete structural deformation where it is not possible to apply deformation measurement sensors, and the DST method can be used for to estimate structural failures where strain and stress sensors cannot be applied. We applied the SDT matrix to a 1D beam, a 2D plate, rotating structures and real wind turbine blades, and successfully estimated the deformation in the structures. However, certain difficulties were encountered while estimating the displacement of brittle material such as an alumina beam. The study aims at estimating the displacement and stress to predict the failure of the structure. We also explored applying the method to multi-material structures such as a two-beam bonded structure. In the study, we used alumina–aluminum bonded structures because alumina is bonded to the substrate to protect the structure from heat in many cases. Finally, we present the results of the displacement and failure estimation for the alumina–aluminum structure. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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20 pages, 12209 KiB

Open AccessArticle

MFL-Based Local Damage Diagnosis and SVM-Based Damage Type Classification for Wire Rope NDE

by Ju-Won Kim, Kassahun Demissie Tola, Dai Quoc Tran and Seunghee Park

Materials 2019, 12(18), 2894; https://doi.org/10.3390/ma12182894 - 7 Sep 2019

Cited by 27 | Viewed by 3445

Abstract

Wire ropes used in various applications such as elevators and cranes to safely carry heavy weights are vulnerable to breakage or cross-sectional loss caused by the external environment. Such damage can pose a serious risk to the safety of the entire structure because damage under tensile force rapidly expands due to concentration of stress. In this study, the magnetic flux leakage (MFL) method was applied to diagnose cuts, corrosion, and compression damage in wire ropes. Magnetic flux signals were measured by scanning damaged wire rope specimens using a multi-channel sensor head and a compact data acquisition system. A series of signal-processing procedures, including the Hilbert transform-based enveloping process, was applied to reduce noise and improve the resolution of signals. The possibility of diagnosing several types of damage was verified using enveloped magnetic flux signals. The characteristics of the MFL signals according to each damage type were then analyzed by comparing the extracted damage indices for each damage type. For automated damage type classification, a support vector machine (SVM)-based classifier was trained using the extracted damage indices. Finally, damage types were automatically classified as cutting and other damages using the trained SVM classifier. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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11 pages, 3047 KiB

Open AccessArticle

A Study on Fatigue State Evaluation of Rail by the Use of Ultrasonic Nonlinearity

by Bo Zhu and Jaesun Lee

Materials 2019, 12(17), 2698; https://doi.org/10.3390/ma12172698 - 23 Aug 2019

Cited by 10 | Viewed by 2940

Abstract

Nonlinear ultrasonic testing has been accepted as a promising manner for evaluating material integrity in an early stage. Stress fatigue is the main threats to train safety, railways examinations for stress fatigue are more significant and necessary. A series of ultrasonic nonlinear wave experiments are conducted for rail specimens extracted from railhead with different degree of fatigue produced by three-point bent loading condition. The nonlinear parameter is the indicator of nonlinear waves for expressing the degree the fatigue. The experimental results show that the sensitivity of a third harmonic longitudinal wave is higher than second harmonic longitudinal wave testing. As the same time, collinear wave mixing shows strong relative with fatigue damages than a second longitudinal wave nondestructive testing (NDT) method and provides more reliable results than third harmonic longitudinal waves nonlinear testing method. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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19 pages, 10142 KiB

Open AccessArticle

Numerical and Experimental Research on Identifying a Delamination in Ballastless Slab Track

by Guopeng Fan, Haiyan Zhang, Wenfa Zhu, Hui Zhang and Xiaodong Chai

Materials 2019, 12(11), 1788; https://doi.org/10.3390/ma12111788 - 2 Jun 2019

Cited by 14 | Viewed by 2777

Abstract

This paper aims to adopt the total focusing method (TFM) and wavenumber method for characterizing a delamination in ballastless slab track. Twelve dry point contact (DPC) transducers located at the upper surface of the slab track compose a linear array. These transducers are employed to actuate shear waves, which are suitable for identifying the delamination. The technique of removing the surface wave has been implemented for only retaining the scattered wave caused by the delamination and the reflected wave from the bottom of bed plate. Numerical and experimental results demonstrate that the delamination and bottom of the bed plate can be identified by the proposed methods. Furthermore, the near-surface pseudomorphism is distinctly restrained after removing the surface wave. Compared to TFM, the wavenumber method has the great advantages of improving computational performance and lateral resolution. However, they have no significant difference in the longitudinal resolution. Furthermore, it has been confirmed that the lateral resolution can be affected by the amount of transducers. This paper can provide valuable suggestions on improving the computational performance and the imaging accuracy when we identify a delamination in ballastless slab track. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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21 pages, 7082 KiB

Open AccessArticle

Enhanced Sensing and Data Processing System for Continuous Profiling of Pavement Deflection

by Boo Hyun Nam, Kenneth H. Stokoe II and Heejung Youn

Materials 2019, 12(10), 1653; https://doi.org/10.3390/ma12101653 - 21 May 2019

Cited by 3 | Viewed by 2547

Abstract

Continuous pavement deflection profiling in a nondestructive manner has received great attention because of its efficiency in pavement evaluation. The Rolling Dynamic Deflectometer (RDD) is a continuous pavement deflection profiling technology and has demonstrated its successful use at many pavement projects. However, RDD’s current test speed of 1.6 km/h (with the prototype rolling sensor) often limits its use in large-coverage projects and traffic congested areas. Increasing the test speed creates a higher-noise environment, lowered signal-to-noise ratio, and sensor decoupling with the ground surface. This study presents the enhancement to the RDD for increased test speed, associated with the new design of the lower-level rolling sensor and higher-performance digital filter and data processing. The new sensor along with the enhanced data processing could increase the spatial resolution of the deflection data, which allows the increase of the test speed of the RDD. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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15 pages, 5097 KiB

Open AccessArticle

Attenuation of a Slow Subsonic A₀ Mode Ultrasonic Guided Wave in Thin Plastic Films

by Rymantas Kažys, Reimondas Šliteris, Liudas Mažeika, Olgirdas Tumšys and Egidijus Žukauskas

Materials 2019, 12(10), 1648; https://doi.org/10.3390/ma12101648 - 21 May 2019

Cited by 8 | Viewed by 3454

Abstract

The ultrasonic testing technique using Lamb waves is widely used for the non-destructive testing and evaluation of various structures. For air-coupled excitation and the reception of A₀ mode Lamb waves, leaky guided waves are usually exploited. However, at low frequencies (<100 kHz), the velocity of this mode in plastic and composite materials can become slower than the ultrasound velocity in air, and its propagation in films is accompanied only by an evanescent wave in air. To date, the information about the attenuation of the slow A₀ mode is very contradictory. Therefore, the objective of this investigation was the measurement of the attenuation of the slow A₀ mode in thin plastic films. The measurement of the attenuation of normal displacements of the film caused by a propagating slow A₀ mode is discussed. The normal displacements of the film at different distances from the source were measured by a laser interferometer. In order to reduce diffraction errors, the measurement method based on the excitation of cylindrical but not plane waves was proposed. The slow A₀ mode was excited in the polyvinylchloride film by a dry contact type ultrasonic transducer made of high-efficiency PMN-32%PT strip-like piezoelectric crystal. It was found that that the attenuation of the slow A₀ mode in PVC film at the frequency of 44 kHz is 2 dB/cm. The obtained results can be useful for the development of quality control methods for plastic films. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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11 pages, 2442 KiB

Open AccessArticle

NDE Detection Techniques and Characterization of Aluminum Wires Embedded in Honeycomb Sandwich Composite Panels Using Terahertz Waves

by Kwang-Hee Im, Sun-Kyu Kim, Jong-An Jung, Young-Tae Cho, Yong-Deuck Woo and Chien-Ping Chiou

Materials 2019, 12(8), 1264; https://doi.org/10.3390/ma12081264 - 17 Apr 2019

Cited by 5 | Viewed by 2650

Abstract

For many years, scientists have been aware of the importance of terahertz waves (T-rays), which have now emerged as an NDE (nondestructive evaluation) technique for certain ranges of the electronic spectrum. The present study deals with T-ray scanning techniques of honeycomb sandwich composite panels with a carbon-fiber-reinforced plastic (CFRP) skin as well as the refractive index (n), and the electrical conductivity (α) of glass fiber-reinforced plastic (GFRP) composites. For this experiment, the degree of penetration to FRP composites is investigated for the THz transmitted power based on the angle in the electric field (E-field) direction vs. the direction of the unidirectional carbon fibers. Also, when CFRP skin honeycomb sandwich panels are manufactured for use in aerospace applications, aluminum wires are twisted together into the one-sided surface of the honeycomb sandwich panels to protect against thunderstorms. The aluminum wires are partly visible because they are embedded in the CFRP skin on the honeycomb sandwich panels. After finishing work with a paintjob, the wires become invisible. Thus, detecting the aluminum wires is a key issue for product monitoring. Based on a simple resistor model, an optimal scanning method is proposed to determine the preferred scan orientation on the baseline of the E-field in the direction of fibers to evaluate the level of transmission of T-rays according to the frequency bandwidth. Thus, the combination of angles required to detect the aluminum wires embedded with carbon fibers on the surface of the composite panels can be determined. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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12 pages, 2293 KiB

Open AccessArticle

Inspection of Reactor Steel Degradation by Magnetic Adaptive Testing

by Gábor Vértesy, Antal Gasparics, Ildikó Szenthe, Ferenc Gillemot and Inge Uytdenhouwen

Materials 2019, 12(6), 963; https://doi.org/10.3390/ma12060963 - 22 Mar 2019

Cited by 8 | Viewed by 3079

Abstract

Degradation of nuclear pressure vessel steel materials, 15Kh2NMFA type and A508 Cl2 type (definition is given in the text) were investigated by a novel magnetic nondestructive testing method, so-called Magnetic Adaptive Testing (MAT), which is based on systematic measurement and evaluation of minor magnetic hysteresis loops. The measured samples were thermally treated by a special step cooling procedure, which generated structural changes in the material. It was found that this type of degradation can be easily followed by magnetic measurements. Charpy impact test were also performed and the results were compared with the magnetic parameters. In case of 15Kh2NMFA steel, a good, reliable and closely linear correlation was found between magnetic descriptors and transition temperature. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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12 pages, 5677 KiB

Open AccessArticle

Magnetostrictive Guided Wave Technique Verification for Detection and Monitoring Defects in the Pipe Weld

by Se-Beom Oh, Yong-Moo Cheong, Deok-Hyun Lee and Kyung-Mo Kim

Materials 2019, 12(6), 867; https://doi.org/10.3390/ma12060867 - 15 Mar 2019

Cited by 8 | Viewed by 3004

Abstract

During inspection of piping in nuclear power plants or other industries, it is difficult to implement conventional nondestructive techniques due to limited accessibility or obstacles such as pipes with insulation, pipes buried underground, structural complexity, or radiation environments. In addition, since the defects mainly occur in the weld region or support area, it is not easy to separate defect signals from those of structural components. To solve these problems, we developed a technique to detect and monitor the formation and growth of defects, using a magnetostrictive guided wave sensor. This sensor has advantages (such as sharp and clear signal patterns and ability to easily eliminate the signal from the geometric structure) over the conventional piezoelectric transducer. To verify our technique, signals from actual pipe welds with defects were acquired and processed with our phase matching/subtraction program. The proposed technique shows a superior capability for detection and monitoring of defects, compared to the conventional guided wave methods. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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15 pages, 3501 KiB

Open AccessArticle

Nonlinear Acoustic Modeling and Measurements during the Fatigue Process in Metals

by Wenhan Lyu, Xianmei Wu and Weijiang Xu

Materials 2019, 12(4), 607; https://doi.org/10.3390/ma12040607 - 18 Feb 2019

Cited by 6 | Viewed by 2813

Abstract

The nonlinear spring model combined with dislocation dipole theory was applied to describe the acoustic nonlinearity during the fatigue process in metals. The spring stiffness changes with fatigue degree. For the early stage, spring stiffness approaches infinity, and the heavier nonlinearity mainly results from the increase of dislocation density. Further fatigue leads to the occurrence of micro-cracks, during which spring stiffness begins to decrease. Abundant micro-crack sprouting accelerates the crack’s expansion, and spring stiffness drops quickly, which causes the obvious decline in the transmitted harmonic amplitudes. Solutions obtained from the nonlinear wave equation with dislocation terms were added into the spring model. Varying spring stiffness was chosen for simulating the fatigue process. Then, nonlinear harmonic variation during this process was observed, which was classified into three stages: (I) the early dislocation fatigue stage; (II) the micro-crack sprouting stage; (III) the crack expansion stage. Nonlinear acoustic measurements were carried out on an aluminum alloy specimen during its fatigue process until cracks could be seen clearly. Harmonic variations in experiments can also be classified into the same three stages as the numerical results, which provides a theoretical and experimental reference for fatigue evaluation in metals using the nonlinear acoustic method. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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17 pages, 13250 KiB

Open AccessArticle

Computation of Propagating and Non-Propagating Lamb-Like Wave in a Functionally Graded Piezoelectric Spherical Curved Plate by an Orthogonal Function Technique

by Xiaoming Zhang, Shunli Liang, Xiaoming Han and Zhi Li

Materials 2018, 11(12), 2363; https://doi.org/10.3390/ma11122363 - 23 Nov 2018

Cited by 3 | Viewed by 2512

Abstract

Non-propagating waves have great potential for crack evaluation, but it is difficult to obtain the complex solutions of the transcendental dispersion equation corresponding to the non-propagating wave. This paper presents an analytical approach based on the orthogonal function technique to investigate non-propagating Lamb-like waves in a functionally graded piezoelectric spherical curved plate. The presented approach can transform the set of partial differential equations for the acoustic waves into an eigenvalue problem that can give the generally complex wave numbers and the field profiles. A comparison of the obtained results with the well-known ones in plates is provided. The obtained solutions of the dispersion equation are shown graphically in three dimensional frequency-complex wave number space, which aids in understanding the properties of non-propagating waves better. The properties of the guided wave, including real, purely imaginary, and complex branches in various functionally graded piezoelectric spherical curved plates, are studied. The effects of material piezoelectricity, graded fields, and mechanical and electrical boundary conditions on the dispersion characteristics, are illustrated. The amplitude distributions of displacement and electric potential are also discussed, to analyze the specificities of non-propagating waves. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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12 pages, 2401 KiB

Open AccessArticle

Combination of Phase Matching and Phase-Reversal Approaches for Thermal Damage Assessment by Second Harmonic Lamb Waves

by Weibin Li, Shicheng Hu and Mingxi Deng

Materials 2018, 11(10), 1961; https://doi.org/10.3390/ma11101961 - 12 Oct 2018

Cited by 21 | Viewed by 2926

Abstract

It is known that measurement and extraction of the tiny amplitude of second harmonic Lamb waves are the main difficulties for practical applications of the nonlinear Lamb wave technique. In this study, phase-reversal approaches and phase matching technique are combined to build up the second-harmonic generation (SHG) of Lamb waves. A specific Lamb wave mode pair, which satisfied phase matching conditions, is selected to ensure the generation of cumulative second harmonic waves. Lamb wave signals with the same frequency but in reverse phase, propagating in the given specimen, are added together to counteract the fundamental waves, and simultaneously to enhance the signals of the second harmonic generated. The obtained results show that the phase-reversal approach can enhance the signals of second harmonic Lamb waves, and effectively counteract that of the fundamental waves. The approach is applied to assess the thermal-induced material degradation in the stainless steel plates. Distinctions of the acoustic nonlinearity parameters under different degraded levels are clearly shown in an improved repeatable and reliable manner, while those of linear wave velocity in the specimens are neglectable. The experimental investigations performed indicate that the proposed approach can be taken as a promising alternative for assessment of material degradation in its early stages. Full article

(This article belongs to the Special Issue Non-destructive Inspection)

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